Build Thread Scratch build electric tethered car racer

[WickedFog]

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So I tickled the throttle and despite the lesser gear reduction 1:1.33 and larger diameter wheels we get wheel spin!

I had to clean the marks off the cream carpet quickly before the boss noticed and before I took the picture.

Oops.

This is a bit of a concern, may have to build up speed really gently at the next track test.

Dial the punch setting way down in your ESC.

 

[Roog]

Dial the punch setting way down in your ESC.

Thanks for the suggestion @WickedFog it’s the first time I have plugged the control panel in since my original set up back in December last year. I had to check the manual.

I have now set it to Level 1 ‘softest setting’ from the previous ‘middling’ level 3, mind you it still spins up smart-ish when off load.

Note to self, when making next model make sure the control panel port on the ESC is in an accessible position!

 

[WickedFog]

Note to self, when making next model make sure the control panel port on the ESC is in an accessible position!

Lol, yeah, been there before.

There also is a setting in some radios called EXP (Exponent). It changes your throttle curve and allows you to lower the response of the trigger when you are at minimal trigger pull. Standard is just a linear throttle curve. Maybe adding a more dynamic curve will make it easier to manage your spinning.

 

[ahr43]

"Softening" the start mode (aka Punch) will definitely help reduce tire spin.

+1 with what Kevin says. Setting in a negative expo will delay power delivery until later in the trigger pull. As an option to expo, check your radio to see if it has a 'Throttle Speed' option. This too will move the place trigger pull brings in a bang-on throttle. Personally, for me in RC drag racing, adjusting expo brings the power on in a more linear, manageable, manner. Throttle speed tends to bang-in when it comes on inducing either excessive wheel spin or fishtailing.

Good luck, mate. -AC

 

[Roog]

"Softening" the start mode (aka Punch) will definitely help reduce tire spin.

+1 with what Kevin says. Setting in a negative expo will delay power delivery until later in the trigger pull. As an option to expo, check your radio to see if it has a 'Throttle Speed' option. This too will move the place trigger pull brings in a bang-on throttle. Personally, for me in RC drag racing, adjusting expo brings the power on in a more linear, manageable, manner. Throttle speed tends to bang-in when it comes on inducing either excessive wheel spin or fishtailing.

Good luck, mate. -AC

Good idea, I have tinkered with the exponential function previously I’m not sure if I applied negative values though?

I’ll revisit this.

 

[Roog]

Here it is ready for its next run, oh the anticipation!

Well the good news is the tires stayed on throughout the three runs, hoorah! Unfortunately there was that vibration again at 60mph, easing in more throttle did nothing but make the sound louder and the very clear smell of burning rubber greater! Motor and battery ‘cool as a cucumber’, I hope that translates across the pond OK!. It seems like the drive wheels are fighting a braking force that keeps pace with the power input.

I am not sure what is causing the issue, I did wonder whether it was due to the simple plain bearing setup, but why would this lead to the rear tires burning up?

I noticed that the car leaves quite strong tire marks on the track and that these stop at places on the circle, so it seems to be taking off over the slight dips in the track.

When I got it home I noticed that the front suspension arm pivot pin was lose, this might have caused oscillation in the front wheel leading to drag and therefore the drive wheels simply driving against a front wheel brake.

I am going to lock out the front suspension next time to see if this stops the vibration and whilst this might lead to a rougher run perhaps it will solve the limiting vibration issue. Then I might consider building a ball race rear shaft, I’m just not sure it’s worth it.

I am thinking of building a scale model, that way I have an excuse for it going slowly, this speed game is getting me down.

 

[WickedFog]

I wonder if not having a rear diff might be causing the vibration. Do the other guys use a diff in their cars?

If you could mount a gopro to the center pole that wasable to rotate with the car, you can get decent slowmo footage with them. Maybe you could better see what is going on.

Or mount one in the car, looking at the rear setup, and one looking at the front wheel assembly.

 

[Roog]

I wonder if not having a rear diff might be causing the vibration. Do the other guys use a diff in their cars?

If you could mount a gopro to the center pole that wasable to rotate with the car, you can get decent slowmo footage with them. Maybe you could better see what is going on.

Or mount one in the car, looking at the rear setup, and one looking at the front wheel assembly.

I don't think I have seen any car with a diff, the our guy who runs IC cars at the track definitely gets away with a fixed axle and his cars have a greater distance between the inside and out side wheels. It seems to be an accepted limitation, plus we do have cars that lift their inside wheels and under those circumstances they would loose all drive if they had a diff.

I like the idea of a go pro, there really isn't any thing to see from the side of the track, just the smell of burning rubber at a certain speed! We couldn't detect an overspeed at the moment the car stops leaving black trails.

I did wonder if it was the drive belt being thrown out of the circle trying to ride up on the pulley rim? but there isn't any wear/ damage to the belt that I can see.

One other thing that we did was to shorten the tether cable as this was previously causing my car to not only travel further per lap but also to run on the out side edge of the track which is less smooth, alas this didn't make a big difference.

I am going to try again with the front suspension completely locked down or with a short section of heavy duty rubber fuel tube from a full sized vehicle as a damper instead of a spring.

Perhaps the track is just too tight (and bumpy) to go much faster? that does sound like cop out though.

Still, no worries I will keep plugging away at this and it does give me an excuse the build another car (a slower scale one) because following my first visit to the track last year to accompany an old friend it was really was just about joining in. Like all of these things you get grand ideas and an ambition to go faster! Despite my poor showing I still hold our track record!

Hey i could use my electric pack to build an RC car!

Oh and I just wanted to say this again, after 4 months of trying different tires and wheels, this time I did not have a tire leave its rim or go a funny shape!

 

[WickedFog]

I guess your rear tires should wear accordingly to account for the outside tire traveling further. I would think eventually the inside tire would wear to be ever so slightly smaller in diameter.

It could be the bumpy track causing it. But adding a gopro so you can see what your car is doing should quickly show you what is causing this. Even if you have to run it with the body off to get some good footage.

 

[Roog]

I guess your rear tires should wear accordingly to account for the outside tire traveling further. I would think eventually the inside tire would wear to be ever so slightly smaller in diameter.

It could be the bumpy track causing it. But adding a gopro so you can see what your car is doing should quickly show you what is causing this. Even if you have to run it with the body off to get some good footage.

It was the out side tire that showed the wear and significant wear at that. Both were coated with the green paint from the track, likely wheel spin, inside wheel lifting?

 

[WickedFog]

May be. Can you raise your attachment point for the tether? If not, I would maybe think about cutting some pockets in the vertical rib of your aluminum angle to lower your center of gravity. There is a way to test your center of gravity. I would find where that point is and attach the tether there, or at least try to adjust the center of gravity to get it as close to the tether attachment point as possible.

 

[Roog]

May be. Can you raise your attachment point for the tether? If not, I would maybe think about cutting some pockets in the vertical rib of your aluminum angle to lower your center of gravity. There is a way to test your center of gravity. I would find where that point is and attach the tether there, or at least try to adjust the center of gravity to get it as close to the tether attachment point as possible.

Nice demo, I'll give it a go, front to back I have it figured, height wise less so.
Interestingly for me at least, I did run the car with the tether connection slightly behind the COG (1st time out second run), when I was using temporary tether strap, (my 1st one bent!) it seemed happier.

Of course , with a tether car you can just hang it from its tether.

 

[Doom!]

Now that you've got the tire issues settled, I think it will be easier to nail down the rest of it. Hopefully a loose front tire was the issue, but it never seems to be that simple does it. Don't lose heart, you've got this, take a break and come back to0 it with fresh eyes.

 

[Roog]

Ok, due to poor weather its been two months since I last visited the track, this changed yesterday.

The good news is that locking off the front suspension and loosening the tooth belt, (it was tight) seems to have stopped the terrible howling noise at speeds above 50mph, however its new top speed is still only a fraction better at 66 and bit mph. It sounded and looked very smooth with no dramas, the group are beginning to wonder if the small diameter of the track is a limiting factor to top speed. Squeezing the throttle further just results in rubber traces on the track and no greater speed, the car even sounds faster, but the speed meter which counts the laps shows that it isn't.

Apparently, visiting proven fast cars don't perform well at the track either.

I am waiting on some new bevel gears to start the design of my next project a Nitro powered car, the plan is to make a semi scale 1950's formula 1 car. I might paint it red and call it a Ferrari LOL!

So I plan to continue to run my electric 'angle iron' until my Nitro car is ready, but I don't expect much improvement and because I have done well not to trash the motor ESC and battery in the various mishaps I've had I don't want to kill them trying. I am sure that I will find a use for them in a future project. Who knows it might be an RC car!

Otherwise I will start a new thread over in the nitro section to cover the build of my next dizzy effort :0)

 

[ahr43]

Red? Ferrari? What? No BRG - British Racing Green with yellow gold wheels, ala Lotus? Blasphemy!

j/k. Nitro tether sounds like a great follow-on project to complement your successful electric project. Anxious to see how you engine it. .12 or .18 or .21 or ?

Cheers, mate. -AC

 

[Roog]

The Engine is a 0.20 Irvine, it was more or less gifted to me so I feel obliged to use it for all of its failings!

I feel that British Racing Green is a bit over used over here, a lot of British made sports cars were painted in this colour so bright red is quite a nice contrast.

I am looking at classic racers so that would include the Indie cars of the 50's too, now some of them had interesting colour schemes. At the moment I am planning around a particular wheel base/chassis length and the choice of body and colour scheme is up for grabs.

 

[WickedFog]

I wonder if you could turn the front wheel slightly and get it to go any faster

 

[Roog]

I wonder if you could turn the front wheel slightly and get it to go any faster

Agreed, its a thought, I can make fine adjustments and try again!

Whilst the car is now well balanced with the tether attachment point aligning with the car centre of gravity it has a habit of over steering during start up, especially on the damp course we had yesterday, probably due to slight wheel spin but once up and running it was the most stable I have seen it. It would be nice to squeeze 70mph out of it, our max legal limit.

 

[WickedFog]

Agreed, its a thought, I can make fine adjustments and try again!

Whilst the car is now well balanced with the tether attachment point aligning with the car centre of gravity it has a habit of over steering during start up, especially on the damp course we had yesterday, probably due to slight wheel spin but once up and running it was the most stable I have seen it. It would be nice to squeeze 70mph out of it, our max legal limit.

You know what would be wicked? Besides me I mean. Is if you connected a servo to the front wheel. Something super fine and smooth. Maybe you could dial it in on the fly, accounting for traction changes at various speeds.

Or maybe a trailing arm setup, with stabilizers like shocks on it, and a servo adjusting that assembly, controlled by a radio with traction control?

I'll shuddul up now, before we get it to launch rockets at camera drones

On a different note, your rear tires must be doing good huh? I was thinking, they are trying to travel different distances because the inside wheel is travelling around a smaller circle than the outside wheel.

At 80 feet diameter for example, the circumference is 251.3274 feet. If your wheelbase is 6", your outer wheel is travelling a circumference of 252.898 feet. That's a little over 1.5 feet difference in the distance travelled. So in that revolution, both rear tires are going to lose traction. It's a given. With a diff, it would solve a lot of issues. Because this whole fighting between the rear wheels is trying to turn your car right.

You'll always reach a point where the design needs to become more accuracte to the situation to perform better

 

[Roog]

You know what would be wicked? Besides me I mean. Is if you connected a servo to the front wheel. Something super fine and smooth. Maybe you could dial it in on the fly, accounting for traction changes at various speeds.

Or maybe a trailing arm setup, with stabilizers like shocks on it, and a servo adjusting that assembly, controlled by a radio with traction control?

I'll shuddul up now, before we get it to launch rockets at camera drones

On a different note, your rear tires must be doing good huh? I was thinking, they are trying to travel different different distances because the inside wheel is travelling around a smaller circle than the inside wheel.

At 80 feet diameter for example, the circumference is 251.3274 feet. If your wheelbase is 6", your outer wheel is travelling a circumference of 252.898 feet. That's a little over 1.5 feet difference in the distance travelled. So in that revolution, both rear tires are going to lose traction. It's a given. With a diff, it would solve a lot of issues. Because this whole fighting between the rear wheels is trying to turn your car right.

You'll always reach a point where the design needs to become more accuracte to the situation to perform better

This would require a fair bit of modification but I can see how this would be interesting. I will try manual adjustments to see if there is a sign of benefit, could be the answer!